This invention relates to a fiberscope utilizable for optically observing or examining dark places such as the interiors of blood vessels and the heart.
There is a known fiberscope as means for opticaly observing the interiors of blood vessels and the heart, the fiberscope comprising, as shown in FIGS. 1 through 3, a plurality of light guides 9 for transmitting light beams from a light source 3 to a region 5 being observed (the interior of a blood vessel 7 in FIG. 2) through a flexible coating tube 1; an image transmitting fiber 11 equipped with an image focusing lens 19 at the tip thereof, and a liquid guide passage 15 for introducing a physiological saline solution from a syringe 13 and forming a transparent zone by temporarily removing the blood flowing in front of the light guides 9 and the image focusing lens 19 at the tip of the image fiber 11 in the region 5 being observed. In that case, it is needed to secure a physiological saline flush having a flow rate equivalent to that of blood at the tip of the coating tube 1 so as to form the above-described transparent physiological saline solution zone. The liquid guiding passage 15 is unnecessary when a zone without the presence of an opaque solution such as blood is optically probed.
Referring to FIGS. 4 through 7, the construction of the tip of a fiberscope equipped with a conventional liquid guide passage will be described. FIG. 6 is a vertical sectional view of the tip portion. FIG. 4 is a sectional view taken on line A-A' of FIG. 6. FIG. 5 is a sectional view taken on line B-B' of FIG. 6. FIG. 7 is a perspective view of the tip thereof. In those Figures, an image pick-up adaptor 23 for coupling the image focusing lens 19 and the tip of the image fiber 11 is adhesive-bonded and fixed to a recess (reference number 39 of FIG. 10) in a molded tip portion 21 wherein the tips of the light transmitting guides 9 are buried by the method described later. Moreover, the outer face of the molded tip portion 21 and the coating tube 1 are adhesive-bonded and fixed. The coating tube 1 is prepared from polyethylene or vinyl chloride plastics, etc. and about 2.8 mm and 2.2 mm in outer and inner diameters, respectively. The adhesion between the outer face of the molded tip portion 21 and the coating tube 1 is reinforced by filling a coating-tube bonding aperture 25 with an epoxy resin adhesive to deal with an impact at the time of flushing. As shown in FIG. 7, the flush flow 27 is thus formed. The molded tip portion 21 is, as shown in FIG. 6, also slightly positioned back by .DELTA.L.sub.1 from the front face of the coating tube 1 in order to remove the blood from the front face of the image focusing lens 19 and the light guides 9 efficiently.
Referring to FIGS. 8 through 10, subsequently, the method of preparing the aforementioned molded tip portion 21 will be described. As shown in FIG. 8, a fluoroplastic molding die 31 with an aperture 2 mm in diameter and about 10 mm in depth is first prepared and a bundle 33 of plastic fibers for use as light transmitting guides 9 and a fluoroplastic dummy tube 35 for forming the recess (reference number 39 of FIG. 10) in the molded tip portion 21 are inserted into a throughhole 29. The gap between the throughhole 29 of the molding die 31 and the bundle of the plastic fibers 33 as well as the dummy tube 35 is filled with epoxy resin. The profile shown in FIG. 9 is obtained by grinding one end face and removing the molding die 31 from the molded piece 37 after it is hardened. The dummy tube 35 is then pulled out of the molded piece 37 and part of the tube 35 is cut out so that the molded tip portion 21 having the recess 39 may be formed as shown in FIG. 10. FIGS. 11a and 11b illustrate the construction of another conventional fiberscope comprising a molded tip portion 41 having a central aperture for inserting and fixing a pick-up adaptor, liquid guide passages 15 on the left- and right-hand sides and a plurality of light guides 9 for transmitting light, the light guides being buried in an annular form.
The conventional fiberscopes having the construction illustrated in FIGS. 1 through 11 poses the following problems:
(1) The angle of view (.alpha. of FIG. 12) of a fiberscope is determined by the focal length of the image focusing lens and the outer diameter of the image fiber. Although the angle of view may exceed 100 degrees depending on the condition, it is normally about 70 degrees. However, since the angle of illumination (.beta. of FIG. 12), i.e., the maximum angle of opening of illumination is determined by NA (the Numerical Apertures) of the optical fiber as a light guide for transmitting light, it is relatively small when a lens is hardly usable in front of the light guides whose tips are distributed in an annular form as a bundle of optical fibers is used to form the light guides. The numerical apertures is determined by the refractive indices of the core and the clad and, in the case of a fiber for transmitting visible light such as a plastic fiber, its value is 0.6 at the greatest. Consequently, the angle of illumination .beta. is limited to about 50 degrees under liquid such as blood where the fiberscope is mainly intended for use. For that reason, observation is impossible within a region 43 where the angle of illumination .beta. is smaller than that of view .alpha., as shown in FIG. 12.
(2) On the other hand, because the edge of the tip of the conventional fiberscope is obviously sharp, as shown in FIG. 7, it may damage the inner wall of the blood vessel, ureter, etc.
(3) As the outlets of the light guides are one-sided relative to the axial position of the image fiber, there is caused deflection in the distribution of illumination within the visual field. The shortcoming becomes conspicuous particularly when the position of an object being observed is close to the fiberscope.
(4) As the outlet of the liquid guide passage for introducing a flush is one-sided relative to the axial position of the image fiber, there is caused deflection in the visual field by flushing.